Módulo 1 Pediatría Flashcards

Question

A 10-year-old boy is brought to the clinic because of increasing weakness and dyspnea over the past 6 months. He had been healthy and is taking no medications. There is no significant family history of illness. On examination, he appears pale. His hematocrit is 20% and mean corpuscular volume (MCV) is 60/μm3 . Ferritin and total iron binding capacity (TIBC) are within normal levels. Peripheral blood smear reveals basophilic stippling, and capillary lead level is less than 10 μg/dL. Hemoglobin electrophoresis shows an elevation of hemoglobin A2 and an absence of one beta-globin gene. Which of the following is the most likely diagnosis? (A) Elliptocytosis (B) Hemoglobin S-C disease (C) Iron deficiency anemia (D) Lead poisoning (E) Sickle cell anemia (F) Thalassemia

Answer 1

Respuesta: F The **correct answer is F**. Thalassemia refers to any genetic defect in the production of the globin chains of hemoglobin. Patients may have deficient production of the globin beta chain (beta-thalassemia) or the alpha chain (alpha-thalassemia). In the homozygous state, beta-thalassemia (i.e., thalassemia major) causes severe, transfusion- dependent anemia. In the heterozygous state, the beta-thalassemia trait (i.e., thalassemia minor) causes mild to moderate microcytic anemia. Thalassemia minor usually presents as an asymptomatic, mild microcytic anemia, and it is detected through routine blood tests. Usually, the diagnosis of beta-thalassemia minor is suggested by the presence of an isolated, mild microcytic anemia, target cells on the peripheral blood smear, and a normal red blood cell count. An elevation of hemoglobin A2, demonstrated by electrophoresis, confirms the diagnosis of the beta-thalassemia trait. Although basophilic stippling may also be seen in lead poisoning and severe vitamin B12 deficiency, the basophilic stippling in thalassemia results from the retention of ribonucleo-protein particles and mitochondrial remnants in the red blood cells. Elliptocytosis (choice A) is similar to spherocytosis in that it is caused by a defect in a cell wall structural protein and will lead to elliptical red cells on the peripheral blood smear. Hemoglobin S-C disease **(choice B)** is a variant of sickle disease in which the cells carry two abnormal beta-alleles, those for hemoglobin S and those for hemoglobin C. Patients are sometimes severely affected, but generally less so than those with HbSS disease. The normal iron study results (ferritin and total iron binding capacity) exclude iron deficiency anemia **(choice C)** and chronic disorders as the causes of this patient’s microcytic anemia. Patients with thalassemia minor will not experience improvement of their anemia with iron supplementation, and transfusion-related iron overload is a major obstacle of therapy in thalassemia major. Lead poisoning **(choice D)** results from the ingestion or inhalation of lead-containing substances. Chronic exposure results in hypochromic microcytic anemia and basophilic stippling of the when they are greater than 10 μg/dL. This prompts further testing erythrocytes. Screening capillary lead levels suggest lead poisoning for venous lead levels. Sickle cell anemia **(choice E)** is due to a structural defect in hemoglobin that leads to sickling of red cells in conditions of low oxygen tension, low flow, and decreased blood vessel diameter, leading to hemolysis.

Answer 2

Respuesta: B The **correct answer is B**. Urinary tract infections (UTIs) are extremely common in children, especially girls. Failure to diagnose and properly treat UTIs may lead to serious complications, including renal scarring, hypertension, and chronic renal failure. Renal scarring due to UTIs is one of the most common causes of renal failure in children and young adults. UTIs in children younger than 2 years usually present with nonspecific signs and symptoms. Irritability, poor feeding, diarrhea, and fever are the most common manifestations. Occasionally, abdominal tenderness and malodorous urine are present. A diagnosis of UTI becomes more likely in a child with fever (especially if the temperature is higher than 39.0 C) but no identifiable sources of infection. In such cases, urinalysis and urine culture are absolutely necessary to diagnose UTI. Bagged urine specimens are frequently associated with false positive results because of bacterial contamination. Transurethral catheterization is the most widely recommended method of urine collection for UTI screening. Urinalysis and culture are the most important diagnostic investigations in children younger than 2 years who present with unexplained fever. Microscopic examination and culture of stool **(choice C)** or abdominal radiographs **(choice A)** should not be the first diagnostic investigations in cases of fever without an obvious source. Of course, careful history and physical examination are crucial to ruling out causes of fever other than UTIs. Renal ultrasound **(choice D)** is now considered the method of choice to identify obstructive lesions that may predispose to UTIs. Renal ultrasound is performed after a diagnosis of UTI is established. Voiding cystourethrogram **(choice E)** is the most sensitive technique to identify vesicoureteral reflux in children who have had an episode of pyelonephritis.

Answer 3

Respuesta: A The **correct answer is A**. This infant has “late-onset” infant pneumonia, since it occurred more than 1 week after delivery. The most common cause in this setting is coagulase-negative Staphylococcus, which in this setting is usually resistant to oxacillin. Cultures of blood and tracheal aspirates can usually demonstrate the organism. Vancomycin is the initial drug of choice and may sometimes be replaced by a less toxic drug after culture sensitivities become available. Most strains of coagulase-negative Staphylococcus isolated in this setting are resistant, rather than sensitive, to oxacillin **(choice B)**. Group B Streptococcus **(choice C)** is an important cause of early onset neonatal sepsis and pneumonia. Methicillin-sensitive **(choice E)** and methicillin-resistant **(choice D)** Staphylococcus aureus tend to cause skin pustules of the periumbilical and diaper areas.

Answer 4

Respuesta: F The **correct answer is F**. Developmental dysplasia of the hip (DDH) must be diagnosed and treated early in all infants because failure to diagnose it can result in significant morbidity. Physical examination maneuvers, such as the Barlow and Ortolani maneuvers performed in this case, suggest the diagnosis, but further evaluation is undertaken with the use of ultrasound. Ultrasonography is the preferred modality for evaluating the hip and diagnosing DDH in infants younger than 6 months because it directly images the cartilaginous portions of the hip that cannot be seen on plain radiographs. Furthermore, ultrasound examination enables dynamic study of the hip with stress maneuvering. Bone scan **(choice A)** is useful in evaluating early osteomyelitis and bone tumors. Both conditions are unlikely due to the physical examination findings in this patient. CT scan **(choice B)** is often not the first test performed to evaluate infants for DDH. Typically, the diagnosis is confirmed with ultrasound. However, CT scan is very useful for complicated hip dislocations and postoperative hip evaluations. Frog-leg lateral radiographs **(choice C)** describe the hip that is in flexion and externally rotated. They are performed to look for reduction if the hips are displaced or dysplastic. Plain frontal radiographs are performed more commonly, but they have no diagnostic value for DDH in infants younger than 6 months. Joint fluid aspiration **(choice D)** has no place in the evaluation of joint laxity in this infant. It may be performed in cases where a septic joint is suspected. There are, however, no clinical findings to suggest a septic joint in this otherwise healthy infant. Although the patient’s mother has a history of tetracycline ingestion during pregnancy, tetracycline is not a known cause of DDH. Furthermore, serum tetracycline levels **(choice E)** have no diagnostic value in evaluating cartilaginous damage from the exposure.

Answer 5

Respuesta: B The **correct answer is B**. The patient has infectious laryngotracheitis (viral croup), which is caused by the parainfluenza virus. Symptoms are often worse at night and include a characteristic barking cough. Fever is usually low grade, but temperatures as high as 104.0 F have been noted. Epiglottitis is in the differential but is rapidly progressive and is marked by the abrupt onset of high fever. Racemic epinephrine by aerosol has been shown to provide symptomatic relief by vasoconstriction and reduction of local edema. This drug should be used in the moderately ill patient since it may eliminate the need for intubation. Albuterol **(choice A)** would help in treating the bronchospasm but will be of little use in treating croup. In mild illness, humidification may help. Some data support the use of corticosteroids **(choice C)** in severely ill patients, although this remains controversial. Patients given dexamethasone with a repeat dose in 2 hours have had a shorter course of illness than those not given steroids. This is a viral illness, and antibiotics **(choice D)** will be of little utility. However, acute epiglottitis is caused by Haemophilus influenzae type B, and more recently, Group A beta-hemolytic streptococci. A third-generation cephalosporin would be appropriate therapy until culture results are known. Intubation **(choice E)** may be needed if the respiratory distress worsens and epinephrine and steroids fail.

Answer 6

Respuesta: A The **correct answer is A**. Parvovirus B19 is the etiologic agent of this benign exanthem of childhood, which manifests with a “slapped cheeks” facial rash and little or no fever. This exanthema is referred to as fifth disease or erythema infectiosum. B19 parvovirus may cause red cell aplasia (aplastic anemia) in patients with AIDS or with sickle cell disease. Older people develop symmetric polyarthritis **(choice E)**, which is not seen in children. Encephalitis **(choice B)** in immunocompromised patients may have different etiologies. Herpes simplex 1 and 2, herpes zoster, measles, and cytomegalovirus may cause encephalitis in immunocompromised patients. HIV itself frequently affects the CNS, producing subacute encephalitis in AIDS patients. Non-Hodgkin lymphoma **(choice C)** in immunocompromised patients, especially those with AIDS, is most commonly a high- grade B-cell lymphoma. Epstein-Barr virus has been implicated in its pathogenesis. Progressive multifocal leukoencephalopathy (PML) **(choice D)** is a complication of JC virus, a papovavirus that causes no disease in immunocompetent individuals. PML affects patients with AIDS or lymphomas. It is a progressive demyelinating disease in which oligodendroglial cells are destroyed by the virus.

Answer 7

Respuesta: F The **correct answer is F**. Acute otitis media (AOM) is one of the most frequent conditions affecting infants and young children. Accumulation of exudative fluid within the middle ear results in distention of the tympanic membrane and pain. By the age of 3 years, approximately 50% of children will have had at least one episode. Therefore, all primary care physicians should become skilled in the diagnosis of AOM, which entails a careful otoscopic examination. Physical signs of AOM include bulging and fullness of the tympanic membrane with reduced tympanic membrane mobility appreciated under positive pressure. Color change of tympanic membrane **(choice A)** is neither sensitive nor specific of AOM. Fever **(choice B)** is a nonspecific sign that has little correlation with AOM. Children with AOM often have a concomitant upper respiratory infection that justifies temperature elevation. Opacification of tympanic membrane **(choice C)** is no longer considered a useful diagnostic criterion for AOM. Opacification of the tympanic membrane, with resultant absent light reflex, may be also observed in normal ears. Otalgia, or pain localized to the ear **(choice D)**, is absent in a substantial number of cases, especially in infants. Otorrhea **(choice E)** becomes apparent in only 2% of cases, following spontaneous rupture of the tympanic membrane. One should not await this sign to make a diagnosis of AOM.

Answer 8

Respuesta: E The **correct answer is E**. The infant has hydrops fetalis (erythroblastosis fetalis), which is due to severe hemolytic anemia in the fetus or newborn. Some of these infants die in utero of anemia or during delivery of asphyxiation, since they are so anemic that they cannot tolerate hypoxia. Survivors have many problems, including kernicterus (bilirubin levels high enough to damage the brain), congestive heart failure (high output failure secondary to anemia), hepatosplenomegaly (mostly secondary to extramedullary hematopoiesis), and generalized edema. Although, in theory, hydrops fetalis can occur with any severe intrauterine hemolytic anemia, Rh incompatibility (Rh positive fetus in an Rh negative mother) is the most common cause. ABO incompatibility **(choice A)** can cause fetal anemia, but is usually not sufficiently severe to cause the fullblown picture of hydrops fetalis. Beta thalassemia **(choice B)** and sickle cell anemia **(choice D)** do not usually become clinically evident until about the 6th month of life, when the infant completes the switch from making fetal type hemoglobin to adult type hemoglobin. Congenital spherocytosis **(choice C)** can cause anemia at birth, but is usually not sufficiently severe to cause hydrops fetalis.

Answer 9

Respuesta: B The **correct answer is B**. Brachial plexus injuries can occur in neonates who have difficult deliveries with shoulder dystocia, breech extraction, or hyperabduction of the neck. This infant has Erb palsy, which occurs when the upper part of the brachial plexus is injured and causes the signs illustrated in the question stem. Ipsilateral paralysis of the diaphragm may also be present. Sensory changes are usually not present and, if seen, suggest a much more serious tear or avulsion of the brachial plexus. Fortunately, most cases of Erb palsy resolve within 3 months, and the only treatment needed is a protection of the shoulder from excessive motion by immobilizing the arm across the upper abdomen and daily passive range-of-motion exercises performed gently on involved joints starting at 1 week of age. Cases persisting longer than 3 months may require MRI to evaluate both the extent of the injury and the possibility of surgical repair. Bell palsy **(choice A)** causes unilateral facial paralysis, typically in adults. Klumpke paralysis **(choice C)** is due to injury to the lower part of the brachial plexus and causes paralysis of the hand and wrist, often accompanied by ipsilateral Horner syndrome (miosis and ptosis). Like Erb palsy, it can occur during delivery and usually resolves spontaneously in less than 3 months. Passive range-of-motion exercises are the only treatment required. Pseudobulbar palsy **(choice D)** is a degenerative disorder of the nervous system that, over a period of years (often starting in adulthood), causes muscle stiffness and weakness in muscles innervated by the lower cranial nerves and thus produces difficulty swallowing. Spinal cord injury **(choice E)** can result from excessive traction or rotation. It presents with stillbirth or neonatal death due to respiratory failure, especially when the upper cervical cord or lower brain stem is involved. The infant may survive, with weakness, hypotonia, and, later, spasticity, all of which can be mistaken for cerebral palsy. Supranuclear palsy **(choice F)** is a rare disorder of adults with loss of eye movements, muscular rigidity, and difficulty swallowing.

Answer 10

Respuesta: B The **correct answer is B**. This child has infant botulism. Typically, the infant ingests Clostridium spores that germinate and colonize the large intestine, producing a toxin in vivo. This differs from adult botulism, in which preformed toxin in canned foods is ingested. All forms of botulism can be fatal and are considered medical emergencies. Honey is a notorious source of Clostridium spores and is not recommended for children younger than 2 years. Botulism should be suspected in previously healthy infants aged ≤12 months who are constipated and exhibit weakness in sucking, swallowing, or crying, as well as hypotonia, progressive bulbar, and extremity muscle weakness. The major risk is respiratory failure, and approximately 50% of patients require mechanical ventilation during hospitalization. Lumbar puncture and brain imaging generally yield normal results but can help differentiate among other causes of flaccid weakness. The diagnosis is confirmed by finding C. botulinum toxin or organisms in the feces. Antitoxin should be given as promptly as possible because early antitoxin treatment dramatically alters the course of the disease, especially if it is administered within the first 24 hours. In general, therapy with antibiotics **(choice A)** to clear the large bowel of Clostridium in infant botulism is contraindicated because the treatment increases toxin release and worsens the condition. Furthermore, aminoglycosides, such as gentamicin or tobramycin, may potentiate neuro-muscular blockade and are contraindicated. Antiviral medications **(choice C)** have no role in the management of infant botulism. The lumbar puncture performed excluded Guillain-Barré syndrome, which typically shows a high level of protein in the cerebrospinal fluid (especially later in the course of the disease) compared with the reference levels seen in botulism. Corticosteroids **(choice D)**, intravenous gammaglobulin **(choice E)**, and plasmapharesis **(choice F)** are all appropriate choices in the management of Guillain-Barré but are ineffective therapies in the management of infant botulism.

Answer 11

Respuesta: C The **correct answer is C**. Vitamin A, iron, and fluoride can cause acute toxic reactions. Iron is an important ingredient in chewable vitamins. Toxic effects occur after ingestion of 30 mg/kg of body weight and include acute corrosive necrosis of the stomach and acute hepatic necrosis. Deferoxamine, an iron chelator, may be used in treatment. Vitamin D has no significant acute toxicity in the amounts available in chewable tablets, but chronic overuse may cause renal failure **(choice A)**. The most serious toxicity of acetaminophen toxicity **(choice B)** is irreversible hepatotoxicity, which may lead to death. If the presumed ingested dose is less than 100 mg/kg of body weight, the ingestion is mild and need not be treated. Hypervitaminosis A occurs in amounts greater than 300,000 IU, which requires ingestion of 120 chewable tablets. Toxicity leads to an acute elevation of intracranial pressure **(choice D)**. An entire bottle of 100 tablets will need to be ingested to produce fluoride toxicity **(choice E)**. Fluoride should not be administered to infants younger than 6 months. From age 6 months to 3 years, a daily supplement of 0.25 mg of fluoride is recommended if the water has less than 0.3 parts per million concentration.

Answer 12

Respuesta: D The **correct answer is D**. The immunodeficiency disease described is Bruton (X-linked) hypogammaglobulinemia. This condition is due to a defective B-cell specific tyrosine kinase, coded for by the XLA gene, which facilitates proliferation of pre-B cells in the marrow. The immunologic studies detailed in the question stem are typical of this condition. Affected children are vulnerable to recurrent infections that typically begin at about 3 months of age, when the maternal IgG that crosses the placenta is exhausted. Organisms that are likely to be a particular problem in these antibody-deficient children include Haemophilus, pneumococcus, Mycoplasma, Ureaplasma, Campylobacter, Giardia, and enteroviruses. Septic arthritis is a common problem because there are no antibodies coating and protecting the joint surfaces; common causative organisms include Mycoplasma, Haemophilus, and pneumococcus. The other organisms listed are important pathogens in patients with depressed cell-mediated immunity. The fungus Aspergillus **(choice A)** can cause lung infections. Herpes viruses **(choice B)** can cause severe encephalitis. Mycobacterium **(choice C)** can cause lung infections (tuberculosis, atypical mycobacterial infections). Toxoplasma **(choice E)** is a protozoan associated with multisystem infections.

Answer 13

Respuesta: B The **correct answer is B**. This is hypophosphatemic rickets, also known as vitamin D-resistant rickets. This is a usually familial (often with X-linked dominant genetics) and rarely acquired abnormality of phosphate metabolism with impaired renal tubular resorption of phosphate accompanied by decreased intestinal absorption of calcium and phosphate. Vitamin D and parathyroid hormone levels are normal in these cases. The underlying biochemistry can be either impaired renal synthesis of 1,25- dihydroxy-vitamin D3, or impaired cellular response to this substance. Some patients may have only the hypophosphatemia (particularly heterozygous females), whereas others also show severe bone disease. Some patients, as the one in the question, present with craniostenosis (premature suture fusion with resulting abnormal head shape) and seizures before 1 year of age. Other patients present in childhood with bony abnormalities that can include bowed legs, other bone deformities, pseudofractures, short stature, bone pain, and bony outgrowths at muscle attachments that may limit joint motion. This condition can now be treated with combined oral phosphate and 1,25-dihydroxy-vitamin D3. Fanconi syndrome **(choice A)** can have hypophosphatemia as a component, but will show a generalized impairment of renal tubular absorption that also involves glucose, amino acids, and protein. Osteogenesis imperfecta **(choice C)** causes brittle bones that fracture easily. Osteomalacia **(choice D)** is the term used for abnormalities of calcium and phosphate metabolism. It is similar to rickets and affects adults who have reached full stature. Paget disease of bone **(choice E)** is a bony remodeling disease of adults.

Answer 14

Respuesta: E The **correct answer is E**. This girl has pyelonephritis, which is an upper urinary tract infection (UTI) that involves one or both of the kidneys. Children with pyelonephritis present with high fever, dysuria, vomiting, abdominal pain, back pain, and irritability. They often have costovertebral tenderness on examination. The laboratory evaluation often shows leukocytosis. Urinalysis shows the presence of leukocyte esterase, nitrite, and increased white blood cells (>5/hpf). It is also important to note the number of squamous epithelial cells. The urine specimen is considered contaminated and is a poor specimen if there are more than 5 squamous epithelial cells per hpf. Obtaining a urine culture is also important to identify the pathogen and its susceptibility to different antibiotics. In very young children, a clean catch may not be the best method to obtain a good urine sample; straight bladder catheterization may be necessary. The most common organisms are Escherichia coli, Proteus, Klebsiella, and Enterobacter sp. Voiding cystourethrography (VCUG) is indicated in all girls younger than 5 years with the first episode of UTI, because 25 to 30% of such patients have vesicoureteral reflux. Older girls should be evaluated by VCUG after the second episode of UTI. VCUG is also indicated in all boys who have an episode of UTI regardless of age. CT of the abdomen and pelvis **(choice A)** is indicated when there is a suspicion of structural abnormalities of the kidneys, but not for routine evaluation of UTI. IV pyelography **(choice B)** is used to visualize the renal calyces, ureteral anatomy, urinary diversions, and ectopic ureteroceles. It is not routinely recommended after UTI. Plain abdominal radiography **(choice C)** has no role in the evaluation of a known UTI. Radionuclide imaging of the kidneys **(choice D)** involves the administration of a radioactive material, usually99 Tc-DTPA, to assess the blood flow and excretory function of the kidney. Areas of differential function or obstruction can be detected.

Answer 15

Respuesta: E The **correct answer is E**. The shortened PR interval and delta waves with the slow QRS upstroke are classic ECG manifestations of Wolff-Parkinson-White (WPW) syndrome. WPW syndrome is caused by the presence of a tract bypassing the AV node, causing preexcitation and leading to paroxysmal tachycardia. Ablation of the bypass tract is the treatment of choice. An anxiety attack **(choice A)** would present with symptoms of agitation, clamminess, and chest tightness. Lown-Ganong-Levine syndrome **(choice B)** is similar to WPW syndrome, but the PR interval is not shortened. Nodal reentrant tachycardia **(choice C)** would present with P waves following QRS waves. Sinus tachycardia **(choice D)** would not present with the shortened PR interval and QRS waves.

Answer 16

Respuesta: A The **correct answer is A**. Maternal diabetes, particularly poorly controlled type 1 diabetes mellitus, predisposes for large-for- gestational-age (LGA) infants and hypoglycemia in the neonatal period. The latter occurs because the infant’s endocrine system has learned, in utero, to secrete excessively large amounts of insulin in an attempt to regulate its own blood glucose (which is set by the maternal blood). Once the infant is born, serum glucose levels fall rapidly because the mother is no longer supplying the high levels of serum glucose. Some infants are asymptomatic, whereas others may have listlessness, poor feeding, hypotonia, jitters, apneic spells, tachypnea, or seizures. Treatment is with glucose-containing intravenous fluids, which are eventually tapered as enteric feeding progresses. Infants of mothers with hyperthyroidism, such as Graves disease **(choice B)**, may also develop a form of Graves disease secondary to the maternal antibodies to thyroid hormone receptor. Hepatic cirrhosis **(choice C)** is associated with decreased maternal fertility and high rates of spontaneous abortion. Rheumatoid arthritis (choice D) may begin in pregnancy and make delivery difficult, but it does not directly affect the infant. Seizure disorder **(choice E)** in the mother may be complicated to manage during pregnancy because of the teratogenic effects of many of the anticonvulsive drugs. However, it is not the cause of the child’s seizures, which are due to the metabolic disturbance secondary to relative hyperinsulinism. Systemic lupus erythematosus **(SLE; choice F)** in the mother rarely causes neonatal lupus due to circulating maternal autoantibodies. SLE can cause congenital heart block or cutaneous symptoms in symptomatic infants.

Answer 17

Respuesta: G The **correct answer is G**. Serious diarrhea in infants can take two forms: bloody, mucous stools or watery, voluminous stools, which this infant has. The latter is often called secretory diarrhea and, in infants, is most commonly caused by rotavirus and enterotoxigenic Escherichia coli. Severe dehydration and electrolyte imbalances are very dangerous in infants because they may lead to shock, arrhythmias, intracranial hemorrhage, and renal vein thrombosis. Consequently, fluid and electrolyte therapy is the primary and most urgent step. This can be done orally in less ill infants, but it may require peripheral or central intravenous therapy (or even intraosseous administration if a line cannot be started) in those who are more ill. Campylobacter jejuni **(choice A)**, enteroinvasive Escherichia coli **(choice C)**, Salmonella species **(choice H)**, and Shigella species **(choice I)** are all invasive bacteria that infect the large bowel and cause bloody, mucus-laden diarrhea. Examination of the stool in enteroinvasive infections of the large bowel reveals leukocytes, predominantly neutrophils, which in this case were absent. Stool leukocyte count is usually not elevated in viral-mediated and toxin- mediated diarrhea. Cryptosporidium **(choice B)** is a parasite that can cause severe diarrhea in immunocompromised and immuno-suppressed individuals. There is no significant history to suggest that this child is immunosuppressed, and other more common causes of infant diarrhea should be suspected first. Pancreatic insufficiency **(choice D)**, seen in cystic fibrosis, may be a cause of chronic diarrhea when children present with frequent passage of bulky, foul-smelling, oily stools and poor growth pattern. This infant’s growth is normal for his age despite his premature birth, and there is nothing to suggest a chronic cause of his acute presentation of diarrhea. Giardia lamblia **(choice E)** would be an unlikely cause of diarrhea in this child because of the absence of protozoa in the examined stool. Giardia typically causes flatus-associated, foul-smelling stools that float, suggesting fat malabsorption. Lactose intolerance **(choice F)** can cause diarrhea in children after the ingestion of milk. These children often will not gain weight and may even present with failure to thrive. Characteristically, the diarrhea associated with lactose intolerance resolves with fasting. Infants may have temporary lactase deficiency following enteric infections or abdominal surgery, but this deficiency is unlikely to be the primary cause of this child’s diarrhea.

Answer 18

Respuesta: A The **correct answer is A**. This is atopic dermatitis. The presentation illustrated is typical for young children. Secondary bacterial infections and regional lymphadenitis may complicate the clinical picture. The dermatitis often improves by age 3 or 4 years, but periodic exacerbations may continue to occur into adulthood. Older children and adults tend to have more localized lesions, typically with erythema and lichenification. Common sites of involvement in older children and adults include the antecubital and popliteal fossas, eyelids, neck, and wrists. Once the diagnosis is made, the physician must remember not to make the mistake of automatically attributing all subsequent skin lesions the children develop to the atopic dermatitis, since they remain vulnerable to all other dermatologic diseases as well. Cellulitis **(choice B)** is a streptococcal, or less commonly staphylococcal, infection causing acute inflammation of subcutaneous tissues associated with local erythema, tenderness, frequently lymphangitis, and regional lymphadenopathy. The skin is usually warm, edematous, and erythematous, and may exhibit a “peau d’orange” (orange peel) appearance. Contact dermatitis **(choice C)** can resemble atopic dermatitis, but the long history illustrated in the question stem would not be typical of this condition. Lichen simplex chronicus **(choice D)** is characterized by itchy, dry skin that may progress to well-demarcated, hyperpigmented, lichenified plaques of oval, irregular, or angular shape. Seborrheic dermatitis **(choice E)** is an inflammatory scaling disease, usually of the scalp and face, that may initially resemble atopic dermatitis in infants. Unlike atopic dermatitis, however, it tends to remain confined to the head and scalp. (The diaper area may be initially involved, but this usually clears with time.)

Answer 19

Respuesta: D The **correct answer is D**. A technetium bone scan is very effective in diagnosing osteomyelitis in its earliest stages. Technetium uptake reflects osteoblastic activity and skeletal vascularity, so this method is quite sensitive. However, it will give false positive results for fractures, tumors, infarction, or neuropathic osteopathy, and will give false negative results if the vascular supply is impeded in some way. Blood count monitoring **(choice A)** is helpful in monitoring the progress and response to treatment but does not aid in the absolute diagnosis of osteomyelitis. CT scan **(choice B)** would not be as sensitive as an MRI scan, and a technetium scan would be better than either. Gallium scans **(choice C)** are effective in demonstrating response to treatment, but not in the initial diagnosis of osteomyelitis. An x-ray of the foot **(choice E)** will not show osteomyelitis for approximately 1 week.

Answer 20

Respuesta: E The **correct answer is E**. The diagnosis should be easy to make, since the “machinery-like murmur” is classic for patent ductus arteriosus. In premature infants who are not in failure, closure can be achieved medically with the use of indomethacin. Nonpremature infants are less likely to respond, and infants in overt heart failure cannot wait at all and need immediate surgical correction. Indomethacin **(choice A)**, as noted above, is ideal for the premature infant who is not in failure. Digitalis and diuretics **(choice B)** will indeed be used as the infant is rushed to surgery, but, as the question is framed, they alone cannot correct the problem. The infant does not have either an atrial septal defect **(choice C)** or a ventricular septal defect **(choice D)**. Neither of those gives a continuous machinery-like murmur or produces bounding peripheral pulses.

Answer 21

Respuesta: A The **correct answer is A**. Physiologic leukorrhea is the most likely diagnosis. It frequently occurs a few months prior to menarche. Menarche may occur at Tanner stage III, usually about 1 year following the peak height velocity. The onset of menarche seems imminent in this girl. The pH of vaginal fluid falls below 4 with the onset of puberty. Certain vaginal infections alter the pH. For example, both trichomoniasis and bacterial vaginosis are characterized by a pH of greater than 5. There is no evidence of abnormal vaginal discharge, either by amount, color, or odor. No inflammation of the perineum is evident. Discussion of hygiene and possible irritants **(choice B)** is particularly appropriate for prepubertal girls who have symptoms of dysuria or perineal irritation from bubble baths. This does not describe this patient. There are no indications at this time to perform a pelvic examination **(choice C)**. The girl does not have the signs or symptoms of abnormal discharge or vulvovaginitis. A history of sexual contact was not obtained and seems unlikely in this case. Clotrimazole **(choice D)**, miconazole, terconazole, and butoconazole are all commonly used to treat candidal infections. Candida or monilial vaginitis is characterized by clumpy white discharge, described as cottage cheese in appearance. Microscopically, pseudohyphae are seen. None of these are present in this patient. Sitz baths and a mild strength hydrocortisone cream **(choice E)** may be helpful in soothing an irritated or mildly inflamed vulva. These are sometimes recommended as treatment for types of dermatitis, such as contact dermatitis, that involve the perineum. This is not necessary in this patient.

Answer 22

Respuesta: B The **correct answer is B**. The patient is losing blood, most likely in the retroperitoneum, as a result of traumatic injury. Her blood pressure is decreased, and she is compensating with an increased pulse. The immediate response is repletion of fluids to counter the hypovolemic shock the patient is experiencing. Perfusion to the brain and heart is of utmost importance. The broken arm will need to corrected after she has been surgically stabilized. The emergency option is to splint the arm **(choice A)**. However, an orthopedic surgeon should evaluate for nerve and vessel damage as well. Although administration of vasopressors may correct the blood pressure, it is not addressing the underlying problem **(choice C)**. The patient has lost blood volume, and pressors will simply clamp down blood supply to the viscera and limbs, leading to ischemic damage. Fluid should be given first, with pressors as an adjunct. The patient is probably losing large quantities of blood and will need replenishment soon **(choice D)**. However, the blood should not be replenished too quickly, as this may lead to worsening shock. Thus, the patient should first be stabilized with fluids; then, blood should be replenished. The underlying problem is a retroperitoneal bleed, and exploratory laparotomy **(choice E)** will be needed to correct the problem. This is a surgical treatment, however, and it is ideal to stabilize the patient’s hemodynamics before the surgical correction.

Answer 23

Respuesta: E The **correct answer is E**. Ewing sarcoma (ES) is the second most common bone cancer in childhood and adolescence. It has a peak age incidence during adolescent years. It rarely occurs in blacks and is more prevalent in boys than girls. ES may have histopathologic features characteristic of neural differentiation; ES is thought to be a tumor of neural origin, whereas most bone tumors are thought to be of mesodermal origin. The tumor category of ES has recently been expanded to include more neural tumors, such as peripheral primitive neuroectodermal tumor. Like other bone tumors, ES is associated with a consistent chromosomal translocation, t(11;22)(q24;q12), which occurs in about 90 to 95% of cases. ES is treated with a multimodal approach, including surgery, chemotherapy, and radiation therapy. ES is a highly radiosensitive tumor. In addition, most patients usually undergo surgery following induction chemotherapy. Chemotherapy is used because most patients who receive local therapy alone will do poorly. Osteosarcoma is treated with chemotherapy and surgery but not radiation. Unlike ES, osteosarcoma is radioresistant.

Answer 24

Respuesta: B The **correct answer is B**. Low-grade reflux can be expected to resolve as the child grows, and the ureteral implantation into the bladder becomes more oblique. While waiting for that to happen, however, the kidney must be protected against infection. Long-term, lowdose antibacterial therapy is thus recommended. The problem is caused by an abnormally short intramural ureteral tunnel rather than bladder neck obstruction. The use of alpha- blockers **(choice A)** is thus not indicated. The goal of therapy is to protect and preserve renal function. To do a nephrectomy **(choice C)** would do the opposite. Spontaneous resolution is expected, but simple reassurance and observation **(choice D)** would leave the kidney unprotected. Surgical correction **(choice E)** is needed in more severe cases in which spontaneous resolution is not likely to occur.

Answer 25

Respuesta: F The **correct answer is F**. Osgood-Schlatter disease is an example of an overuse syndrome associated with physical exertion. It usually occurs around the pubertal growth spurt (ages 10 to 15) before skeletal maturity, when the quadriceps has enlarged but the apophysis has not yet fused with the tibia. The disease results in partial avulsion fracture through the ossification center. Patients complain of pain, tenderness, and a lump over the tibial tubercle. Pain is worsened with contraction of the quadriceps against resistance, and it may be bilateral in some patients. It is a benign, self-limiting condition with rest, immobilization, and gradual return to activity.

Answer 26

Respuesta: A The **correct answer is A**. Acute lymphocytic leukemia (ALL), or lymphoblastic leukemia, is a primary neoplasm of the bone marrow. The malignant cells are immature lymphoblastic cells. Children with ALL generally present with signs and symptoms of bone marrow infiltration and extramedullary disease. Major features are symptoms of bone marrow failure, including anemia, thrombocytopenia, and neutropenia, all of which manifest as fatigue, pallor, petechiae, bleeding, and fever. Additionally, lymphadenopathy and hepato-splenomegaly can reflect leukemic spread. Other signs and symptoms of leukemia include weight loss, bone pain, and dyspnea. The physical examination of children with ALL reflects bone marrow infiltration and extramedullary disease. Patients present with pallor as a result of anemia, petechiae, and bruising secondary to thrombocytopenia, as well as signs of infection because of neutropenia. In addition, leukemic spread may be seen as lymphadenopathy and hepatosplenomegaly Chondromalacia patellae **(choice B)** is the softening of the articular cartilage of the patella. The usual cause is overuse. Chondromalacia patellae is a significant cause of anterior knee pain in teenage girls. Symptoms include retropatellar pain that is worse upon rising from prolonged sitting or when climbing stairs. There may be some degree of patella misalignment, and there is a grating sensation on knee extension. Treatment involves rest and NSAIDs. Ewing sarcoma **(choice C)** is a malignant small cell tumor of long bones that is more common in males less than 20 years of age. It most often occurs around the knee joint, diaphysis of the femur, humerus, tibia, pelvis, and ribs. Ewing sarcoma may mimic an infection, with localized swelling, redness, heat, and fever. There may be both elevated white blood cell count and erythrocyte sedimentation rate.